Ecological magnitude and fine scale dynamics of the mediterranean narrow endemic therophyte,Arenaria provincialis(Caryophyllaceae)

Abstract

Abstract.-In the context of plant species rarity in mediterranean ecosystems, this study aims to precise the autoecology of the local annual endemic plant, Arenaria provincialis (Caryophyllaceae), by quantifying habitat and vegetation characteristics, and demographic parameters. Its populations are surprisingly scattered along a wide altitudinal and topological range, but over small geographical distances. This implies an important habitat differentiation from the thermophilous dry coast to the colder supra-mediterranean summits in open limestone rocky habitats such as steep screes, ledges, cracks or crests. Among the 163 plant species identified in presence of A. provincialis within 100 m 2 area, 92% belong to the stress Grime pole, highlighting the stressful conditions within the different habitats caused by drought, strong wind, and high thermic contrasts. Demographical surveys reveal strong spatial and temporal fluctuations.Key words : annual plant species -autoecology -rocky habitats -endemismdemography.Résumé.-Dans le contexte de la rareté des espèces végétales dans les éco-systèmes méditerranéens, l'objectif de cette étude consiste à préciser l'autoé-cologie d'une plante annuelle endémique, Arenaria provincialis (Caryophyllaceae), en quantifiant les caractéristiques des habitats et de la végé-tation associée ainsi que les paramètres démographiques. Ses populations s'étalent, de manière surprenante, le long d'un large gradient altitudinal, mais sur de petites distances géographiques. Ceci implique une importante différencia-tion des habitats, du littoral sec thermophile aux sommets froids supraméditer-ranéens, au sein d'habitats ouverts, calcaires rocheux tels que les éboulis pentus, les corniches, les anfractuosités des rochers ou les crêtes. Parmi les 163 espèces végétales associées à A. provincialis, sur des surfaces de 100 m 2 , 92% appartiennent au pôle stress des stratégies écologiques de Grime, ce qui met en exergue les conditions stressantes au sein des différents habitats du fait de la sècheresse, de vents forts et d'importants contrastes de température. Les suivis démographiques révèlent de fortes fluctuations spatiales et temporelles.Mots clés : autoécologie -démographie -endémisme -milieux rocheux -plante annuelle.

Factors Underlying the Narrow Distribution of the Mediterranean Annual Plant Arenaria provincialis (Caryophyllaceae)

“…The distance covered by the initial dispersal process is less than one meter, and any secondary dispersal processes are likely to be infrequent because the capsules are trapped between small rocks and particles of gravel. This very limited dispersal capacity was confirmed by the results of a census carried out on 4-m² areas, which showed that the positions occupied by individuals remained practically unchanged year after year, which is quite a surprising finding in view of the fact that A. provincialis has only a short annual life span (Baumel et al 2009): it means that seedlings always take root close to the mother plants. Small dispersal distances are presumably more efficient in rocky habitats such as stone cracks and scree slopes, because they prevent diaspores from reaching unsuitable patches and make it possible for seeds to find free spaces between rocks and to reach down to lower layers of fine substrate.…”

“…data). Given the dense populations of individuals existing on the finest scale (Baumel et al 2009), the presence of a seed bank and the large number of seeds produced by each individual (Table 3), the rarity of A. provincialis does not seem to be attributable to the reproductive capacity of this species.…”

“…It grows in open habitats such as steep scree slopes, ledges, cracks and summit crests, ranging from xero-thermic littoral southwestern sites to cold, northeastern mountain sites (Crouzet 1966;Baumel et al 2009). Arenaria provincialis is protected by French law, European directives and international conventions.…”

“…Biogeographical distribution sensu Pignatti (1982) corresponds to the relative size of the biogeographical region in which species have been reported to occur in the literature (Quézel and Santa 1962;Chater and Halliday 1964;Pignatti 1982;López González 1990). Niche parameter values, regional occupancy and biogeographical distribution range were obtained for 32 species, namely the Arenaria taxa occurring in southern Provence and the most frequent plant species co-occurring with A. provincialis, based on the literature (Molinier 1934;Loisel 1976;Baumel et al 2009) and our own data.…”

“…− Mediterranean Turanean). The species most frequently cohabiting with A. provincialis were determined based on the literature(Molinier 1934;Loisel 1976;Baumel et al 2009) and our own data.…”